Compact vehicle-mounted antenna

ABSTRACT

A compact, vehicle-mounted antenna is disclosed. In one embodiment, a first and second antenna element are positioned on a conductive ground plane. The antenna elements can comprise platforms supported by a ground and a feed. The antenna elements can be tuned to various bands (e.g., cellular or PCS). At least one additional antenna element (e.g., a GPS receive antenna) can be positioned between the two antenna elements. One of the feeds of the antenna elements can be angled so that the antenna element has a desired height (e.g., a height matching the other antenna element). The antenna elements can be electrically connected to a transmission line via a single feed line.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/414,606, filed Sep. 27, 2002, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present disclosure relates to a compact antenna. More specifically,the present disclosure relates to a compact antenna that is suitable foruse with an onboard wireless voice communications and data system.

BACKGROUND

In recent years, there has been an increasing demand for flexible,multi-functional wireless voice and data systems. In the automobileindustry, for instance, new vehicles are often equipped with wirelessvoice and data systems, which communicate with one or more computersonboard the vehicle and are often referred to as “telematics systems.”

A typical telematics system, for example, might provide for wirelesstelephone services. Currently, two major types of wireless telephoneservices predominate the market in the United States: the AdvancedMobile Phone Service (AMPS) and the Personal Communication Service(PCS). A telematics system can typically operate using either of the twoservices depending upon which is available in a particular area. Onefundamental difference between the two services, however, is the band inwhich they operate. AMPS operates in the cellular band between 824 and894 MHz, whereas PCS operates between 1850 and 1990 MHz. Because eachsystem operates in a different band, separate antennas (sometimesreferred to as radiators) are used to transmit and receive the AMPS andPCS signals.

A telematics system might also provide for vehicle positioninginformation using the Global Positioning System (GPS). By receivingtransmissions from orbiting satellites, a GPS receive antenna candetermine an automobile's location within a coordinate reference system.Thus, GPS receive antennas can be used in conjunction with an onboardcomputer to provide a number of driving and mapping services.

As the number of functions performed by onboard telematics systemsincreases, the number of antennas in the vehicle also increases.Additional antennas, however, are often unsightly and difficult toinstall, as they may require additional wiring or modification to thevehicle's body panels. Compounding this problem is the automotiveindustry's increasing emphasis on minimizing the number of parts used invehicle assembly and on internalizing and integrating such electricalcomponents. Other concerns are aesthetic styling considerations forvehicles and ease of installation, whether as anoriginal-equipment-manufacturer (OEM) part or an after-market part.

These issues and concerns are not limited to the automobile industry.Indeed, the desire to integrate and internalize antennas whilemaintaining functionality is one present throughout the wirelessindustries.

SUMMARY

In view of the issues and concerns described above, various embodimentsof a compact, vehicle-mounted antenna are described herein. Thedisclosed features and aspects of the embodiments can be used alone orin various novel and unobvious combinations and sub-combinations withone another.

In one embodiment, an antenna having an antenna element positioned onthe upper surface of a base is disclosed. In this embodiment, aconductive material at least partially covers the base, thereby forminga ground plane. The antenna element of this embodiment includes aplatform substantially parallel to and spaced apart from the groundplane. The antenna element also includes a ground connecting the groundplane to an end of the platform and a feed connecting the base to theplatform. The ground extends substantially perpendicularly from theground plane, whereas the feed includes a portion that is slantedrelative to the base as the feed extends from the base toward theplatform. The feed can be angled so that the antenna element has adesired height. For instance, the feed might be angled so that theantenna element is height-matched to the height of another antennaelement (e.g., a planar-inverted-F antenna) positioned on the base.

In another embodiment, an antenna having an antenna element coupled to aground conductor is disclosed. The antenna element includes a platformsubstantially parallel to and spaced apart from the ground conductor.The platform is supported on the ground conductor by a ground and afeed. In this embodiment, the platform includes a radiating lip thatprojects outwardly over an edge of the ground conductor by apredetermined distance. By extending the radiating lip beyond the edgeof the ground conductor, the lip creates a transition in capacitivecoupling with the edge of the ground conductor that contributes to theimpedance match of the antenna element. The radiating lip can beselectively adjusted (e.g., by being lengthened, shortened, or benteither upwards or downwards) to impedance match the antenna to atransmission line electrically coupled to the antenna element.

In another embodiment, an antenna element formed from a singleconductive strip is disclosed. In this embodiment, the conductive stripis bent and overlapped to form a platform, a sloped segment, and anapproximately vertical segment. The conductive strip is furtherconfigured to transmit and receive electromagnetic transmissions in apredetermined band.

In another embodiment, a multiband antenna having multiple antennaelements is disclosed. The antenna includes a first antenna elementconfigured to transmit and receive electromagnetic transmissions in afirst band, and a second antenna element configured to transmit andreceive electromagnetic transmissions in a second band different fromthe first band. The antenna further includes a conductive feed lineelectrically coupling a transmission line to a first feed of the firstantenna element and a second feed of the second antenna element. Thelength of the feed line between the first feed and the second feedcreates an impedance such that the second antenna element appears to besubstantially an open circuit in the first band. Thus, the first and thesecond antenna elements experience improved electrical isolation fromone another.

In another embodiment, a multiband antenna having multiple antennaelements positioned on a base is disclosed. In this embodiment, the baseincludes a conductive ground surface. A first antenna element positionedon the base is configured to receive and transmit electromagnetic wavesin a first band. The first antenna element includes a first platformthat is substantially parallel to and spaced apart from the groundsurface. The first platform has an inward-facing end and anoutward-facing end, which is directed in a first direction. The firstplatform is supported on the upper surface of the base by a firstsupport and a first feed. The antenna further includes a second antennaelement configured to receive and transmit electromagnetic waves in asecond band. The second antenna element comprises a second platform,which is substantially parallel to and spaced apart from the groundsurface and which also has an inward-facing end and an outward-facingend. Like the first platform, the second platform is supported by aground and a feed. In this embodiment, the outward-facing ends of thefirst and second platforms face substantially opposite directions fromone another.

The antenna can also include at least one additional antenna elementpositioned substantially between the first antenna element and thesecond antenna element on the upper surface of the base. The additionalantenna element can be configured to receive and/or transmitelectromagnetic waves in one or more additional bands. The additionalantenna element can comprise, for instance, a global positioning system(GPS) receive antenna or a satellite radio receiver.

In another embodiment, a vehicle-mounted, communicating antenna havingat least three antenna elements is disclosed. The first antenna elementis for communicating over a first wavelength range. The second antennaelement is for communicating over a second wavelength range differentthan the first wavelength range. The second antenna element is separatedfrom and in general axial alignment with the first antenna element Thethird antenna element is positioned between and in general axialalignment with the first and second antenna elements.

Any of the embodiments disclosed can be utilized in a variety ofapplications. For instance, any of the embodiments or sub-combinationsof the embodiments, can be used as part of an onboard wireless ortelematics system in a vehicle. As part of such systems, the embodimentscan be positioned in various areas of the vehicle. In one embodiment,for instance, the antenna is positioned within a portion of the roofrack. In another embodiment, the antenna is positioned near the interiorrearview mirror assembly and the front windshield of the vehicle.

The foregoing and additional features of the disclosed technology willbe more readily apparent from the following detailed description, whichproceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first perspective view of an exemplary compact, multibandantenna showing three antenna elements mounted to a base.

FIG. 2 is an assembly view of the antenna of FIG. 1 from a bottomperspective view showing the feed line on the bottom surface of the baseand two of the antenna elements in their relation to the base.

FIG. 3 is a side elevational view of the antenna of FIG. 1 FIG. 4 is abottom plan view of the antenna of FIG. 1.

FIG. 5A is a perspective view showing an exemplary embodiment of avehicle roof rack in which the antenna of FIG. 1 is integrated.

FIG. 5B is a perspective view showing an alternative embodiment of theintegrated roof rack and antenna of FIG. 5A.

FIG. 6A is a cross-section in elevation of a first representativeembodiment of the vehicle roof rack and antenna of FIG. 5A.

FIG. 6B is an exploded side view in elevation of the roof rack andantenna of FIG. 6A.

FIG. 6C is a top plan view of a base portion and a bottom plan view of acover portion of the roof rack of FIG. 6A.

FIG. 7 is a cross-section of an integrated vehicle roof rack and antennaassembly according to a second representative embodiment in which theantenna is coupled to the vehicle and the roof rack is in an overlyingrelationship with the antenna.

FIG. 8 is a graph showing the electrical isolation between antennaelements of the exemplary antenna shown in FIG. 1.

FIG. 9 is a cross-section schematically showing an exemplary embodimentof a vehicle interior in which the antenna of FIG. 1 is positionedbetween a windshield and a rearview mirror of the vehicle.

DETAILED DESCRIPTION

Disclosed below are representative embodiments that are not intended tobe limiting in any way. Instead, the present disclosure is directedtoward novel and unobvious features and aspects of the embodiments ofthe compact antenna described below. The disclosed features and aspectsof the embodiments can be used alone or in various novel and unobviouscombinations and sub-combinations with one another.

FIGS. 1-4 show an exemplary embodiment of a compact, multiband antenna10. As best shown in FIG. 1, the antenna 10 includes antenna elements30, 40, 60, which are positioned on a base 20. As illustrated, theantenna elements 30, 40, 60 are aligned along a longitudinal axis, e.g.,a central axis of the base 20. The illustrated base 20 has twosubstantially planar surfaces: an upper surface 22, and a lower surface24. The illustrated base 20 also has lateral edges 26, 28.

In the illustrated embodiment, the base 20 is formed from a printedcircuit board (PCB), which is largely made of an insulative material. Inthis embodiment, the upper surface of the PCB is coated with a suitableconductive material (e.g., copper, tin, etc.), which forms an electricalground plane on the upper surface 22. The illustrated base 20 has arectangular shape, but can be formed into a variety of different shapesdepending on the location in which the antenna 10 is placed or on theparticular application for which the antenna 10 is used.

Antenna element 30 is a first antenna element positioned on the uppersurface 22 of the base 20. In the illustrated embodiment, the antennaelement 30 includes a platform 32 positioned above and spaced apart fromthe ground plane. The platform 32 shown in FIG. 1 is located in a planesubstantially parallel to the ground plane and the upper surface 22.Although the illustrated platform 32 has a generally rectangular shape,the shape of the platform 32 is not limited and can be altered by one ofordinary skill in the art to achieve a variety of performancecharacteristics (e.g., wider or narrower bandwidth, etc.). For example,the width of the platform 32 can be decreased in order to tune theantenna element 30 to a narrower bandwidth. Moreover, the platform 32can include a variety of additional design features known in the artthat impact the antenna element's transmitting and receivingcharacteristics. For example, the platform 32 can include variousapertures or notches that affect the performance of the antenna element30.

The antenna element 30 further includes a ground 34 and a feed 36. Inthe illustrated embodiment, the ground 34 and the feed 36 comprisesingle support structures or posts. In other designs, however, multiplegrounds or feeds can be utilized. The ground 34 shown in FIG. 1 islocated substantially at an inward-facing end of the platform 32 andextends generally perpendicularly from the upper surface to the platform32. The ground 34 is electrically coupled, via solder or other suitablemeans, to the ground plane on the upper surface 22 of the base 20. Asshown more clearly in FIG. 2, the ground 34 can include pegs 35 thathelp affix the antenna element 30 to the base 20 at apertures 78. Asillustrated, the pegs 35 can be formed, e.g., as a single piece, withthe ground 34.

The feed 36 is spaced apart from the ground 34 and, in the illustratedembodiment, similarly extends generally perpendicularly from the uppersurface 22. As shown in FIG. 2, the feed 36 tapers to a feed point 38.The feed point 38 does not contact the ground plane on the upper surface22, but instead connects to the lower surface 24 through a via 74 or asuitable aperture. More specifically, in the illustrated embodiment, theground plane on the upper surface 22 does not cover the area immediatelyadjacent the feed point 38 and the via 74.

In the illustrated embodiment, the antenna element 30 is a quarter-wavethat has a relatively uniform gain in the 360 degrees around theantenna's horizon. The antenna element 30 is configured to transmit andreceive electromagnetic signals in a first band. In the illustratedembodiment, for example, the antenna element 30 is configured to operatein the cellular band, which is between 824 and 894 MHz. In comparisonwith the other communication bands (e.g., PCS), the wavelength of thecellular band is relatively large and, generally speaking, requires alarger antenna element. Moreover, an antenna element configured for thecellular band typically requires a larger ground plane than an antennaelement for a smaller-wavelength band.

In the illustrated embodiment, the antenna element 30 is positionedsubstantially toward the lateral edge 26 of the base 20 (in FIG. 1,toward the right edge of the base 20). The antenna element 30 ispositioned so that an outward-facing edge 39 of the platform 30 does notextend beyond the lateral edge 26 of the base 20. More specifically, theantenna element 30 is positioned so that the area of the ground planebeneath the platform 32 is sufficiently large for the antenna element 30to operate effectively in the cellular band. The particular tuning ofthe antenna element 30, however, is not limited to the cellular band.Instead, the antenna element 30 can be tuned for a variety of otherbands or standards, including, but not limited to: AMPS, PCS (PersonalCommunication System), TACS (Total Access Communication System), NMT(Nordic Mobile Telephone), IS-54/-136 (North American Digital Cellular),IS-95 (North American Digital Cellular), GSM (Global System for MobileCommunications), DSC18000, PDC (Personal Digital Cellular), CDPD(Cellular Digital Packet Data), RAM-Mobitex, Ardis-RD-LaP, Bluetooth, orIEEE 802.11.

The illustrated antenna element 30 is sometimes referred to as aplanar-inverted-F antenna, or “PIFA,” because of its structuralresemblance to the letter “F” on its side (see, e.g., FIG. 2). The shapeof the antenna 30 is not limiting, however, and can be modified in anumber of ways without sacrificing its compact design. For instance, theangles of the feed 36 and the ground 34 relative to the platform 32 andto the upper surface 22 can be altered. Likewise, the locations of thefeed 36 and the ground 34 can be adjusted in a variety of differentways. For instance, one of ordinary skill in the art might adjust theheight of the antenna element 30 (i.e., the distance between theplatform 32 and the ground plane) in order to increase or decrease theradiation resistance or to fit the antenna within a certain space.

As shown in FIG. 1-3, antenna element 40 is a second antenna elementpositioned on the upper surface 22 of the base 20. In the illustratedembodiment, the antenna element 40 includes a platform 42 positionedabove and spaced apart from the ground plane. The platform 42 shown inFIG. 1 is located in a plane substantially parallel to the ground planeon the upper surface 22. Although the illustrated platform 42 has agenerally rectangular shape, this shape is not limited and can bealtered as described above to achieve a variety of performancecharacteristics or to include a variety of additional design features.

Like the antenna element 30, the antenna element 40 includes a ground 44and a feed 46. In the illustrated embodiment, the ground 44 and the feed46 comprise single support structures. In other designs, however,multiple ground posts or feed posts can be utilized. The ground 44 shownin FIG. 1 is located at an inward-facing end of the platform 40 andextends perpendicularly from the upper surface 22 of the base 20. Theground 44 is electrically coupled, via solder or other suitable means,to the ground plane on the upper surface 22. As shown more clearly inFIG. 2, the ground 44 can also include pegs 45 that help attach theantenna element 40 to the base 20 through apertures 80.

As shown in FIG. 3, the feed 46 of the illustrated embodiment is spacedapart from the ground 44 and includes a portion that angles away fromthe ground as it extends from the upper surface 22 to the platform 42.As shown in FIG. 3, for instance, the feed 46 forms an angle θ with theplatform 42 as it extends from the upper surface 22. In the illustratedembodiment, the feed 46 intersects the platform 42 at a location of theplatform 42 near an edge 49, thereby forming a lip portion 47. Further,as shown in FIG. 2, the feed 46 tapers to a feed point 48. The feedpoint 48 does not directly contact the ground plane on the upper surface22, but instead connects to the lower surface 24 of the base 20 througha via 76. By angling the feed 46, the height of the platform 42 can beincreased when compared to the height of an equivalently tuned PIFAwithout detuning the antenna from its desired band or substantiallyaltering the performance of the antenna element 40. The increased heightof the platform 42 allows the antenna element 40 to have a higherradiation resistance, thereby radiating more energy into the free spacearound the antenna element 40. In one particular embodiment, theplatform 42 and the platform 32 are “height matched” such that they areapproximately the same height (e.g., differing by no more than about25-30%) such that the overall dimensions of the antenna can be keptcompact Alternatively, the height of the antenna element 40 can beadjusted to other desired heights. Additional adjustments known in theart may need to be made to the antenna element 40 in order to maintainthe tuning of the antenna element 40 in the desired band (e.g.,narrowing the platform 42).

In the illustrated embodiment, antenna element 40 is configured tooperate in a second band higher than the first band (i.e., a band withhigher frequencies than the first band). For example, the antennaelement 40 can be configured to transmit and receive electromagneticsignals in the PCS band, which is between 1850 and 1990 Mhz. On accountof the antenna element 40 being tuned for a higher frequency, theantenna is generally smaller than the antenna element 30. However, asdiscussed above, the height of the antenna element 40 can be maximizedby angling the feed post 46 without diminishing the antenna element'soverall performance. The antenna element 40 can also be tuned for avariety of other bands or standards, including, but not limited to:AMPS, TACS, NMT, IS-54/-136, IS-95, GSM, DSC18000, PDC, CDPD,RAM-Mobitex, Ardis-RD-LaP, Bluetooth, or IEEE 802.11.

In the embodiment illustrated in FIGS. 1-4, the first antenna element 30is positioned substantially toward the lateral edge 26 of the base 20(in FIG. 1, toward the left edge of the base 20), and the second antennaelement 40 is positioned substantially toward lateral edge 28 of thebase 20 (in FIG. 1, toward the right edge of the base 20). The antennaelements 30, 40 of the illustrated embodiment are also positioned sothat edges 39, 49 of the platforms 32, 42, respectively, facesubstantially opposite directions. In one particular implementation ofthis embodiment, platform edges 39, 49 are positioned so that they areat substantially the farthest possible points from one another allowedby the base 20 and the ground plane. In this implementation, the mutualcoupling between the two antenna elements is effectively reduced.

In the particular embodiment illustrated in FIGS. 1-4 and as best shownin FIG. 3, the antenna element 40 is positioned on the upper surface 22of the base 20 so that the lip portion 47 projects beyond the edge 28 ofthe base 20 by a distance A. In this embodiment, the capacitance betweenthe antenna element 40 and the ground plane is more sensitive to changesin the antenna element 40 design and in the positioning of the antennaelement 40. This increased sensitivity results from the transition incapacitance created between the lip portion 47 and the fringe field atthe edge 28 of the ground plane. Accordingly, the capacitance of theantenna element 40, which partially contributes to the impedance matchof the antenna element 40, can be adjusted by moving the antenna element40 farther from or closer to the edge 28 of the ground plane (e.g., bylengthening, shortening, or bending the lip portion 47 or antennaelement 40 either upward or downward). In other embodiments, however,the antenna element 40 is positioned so that the lip portion 47 does notproject beyond the edge 28, or so that the first antenna element 30 hasa portion of the platform 32 that projects beyond the edge 28 of thebase 10. Typically, however, the antenna element that is tuned for thehigher-frequency band is better suited for such positioning because asmaller ground plane can be used to effectively operate the antennaelement.

The exact dimensions of the antenna elements 30, 40 can vary widely andare not limited to those shown in the figures. Instead, the dimensionsof antenna elements 30, 40 may depend on the space in which the antenna10 is positioned or on the relative placement of other components on theantenna 10. Moreover, the antenna elements 30, 40 can be formed using avariety of construction methods. In the illustrated embodiment, forinstance, the antenna elements 30, 40 are formed from single strips ofconductive material. The conductive material can be any suitableconductor, but in one particular embodiment comprises brass, and can becoated with another material (e.g., tin). Further, the conductivematerial can have a thickness (e.g., 0.02 inches) and malleability thatallows the material to be bent and shaped. In one embodiment, forexample, the antenna elements 30, 40 are originally elongated, flat,substantially rectangular strips that have the grounds 34, 44 shaped atone end and the feeds 36, 46 shaped at the other. The strips are thenbent and folded to form the antenna elements 30, 40. One or more foldingtabs 50 (one being shown on the antenna element 30 in FIG. 2) can beused to secure the antenna elements 30, 40 into their final shape.Additionally, the strip can include a tongue and slot combination 52(shown on antenna element 40 in FIG. 2) to further secure the antennaelements 30, 40 into their final shape. This particular method ofconstruction is not limiting, however, and a number of other methodsknown in the art can be used (e.g., casting, forging, milling, etc.).

FIG. 4 is a bottom view of the base 20 of the antenna 10 showing thefeed line 70 that is used to electrically connect the first antennaelement 30 and the second antenna element 40 to the transmission line(not shown). In the illustrated embodiment, the feed line 70 comprises amicrostrip trace on the bottom of the PCB that forms the base 20. Thefeed line 70 originates at a transmission line connection 72 thatelectrically couples the feed line 70 to the transmission line. Thetransmission line can be a coaxial cable that carries the relevantsignal (e.g., an analog RF signal) and can be connected to a variety ofelectrical components that process and produce the signal, including,but not limited to, an onboard computer, telephone system, or othercentral control circuit. The illustrated feed line 70 is designed tofeed both antenna elements 30, 40, thereby reducing the number of wiresthat need to be routed and connected to the antenna 10. Thus, forinstance, if the antenna 10 is used in a motor vehicle, antenna elements30, 40 can be driven using a single transmission line, therebysimplifying the installation process and minimizing the overall amountof wiring in the vehicle.

As shown in FIG. 4, the feed line 70 is electrically coupled to thefirst antenna element 30 at a first feed point 74, and to the secondantenna element 40 at a second feed point 76. Thus, the illustrated feedline 70 is separable into a first segment 70A between the transmissionline connection 72 and the first feed point 74, and a second segment 70Bbetween the first feed point 74 and the second feed point 76. Theillustrated feed line 70 can be designed to facilitate impedancematching of the antenna elements 30, 40 so that they are independent ofeach other as much as possible. For example, in order to achieve adesired electrical isolation, the length of the second segment 70B(i.e., the distance between the first feed point 74 and the second feedpoint 76) can be adjusted to a length such that the antenna element 40for the second band presents what appears to be substantially an opencircuit at the frequency of the first antenna element 30. For example,in one embodiment where the antenna elements 30, 40 are tuned to thecellular and PCS bands, respectively, the cellular antenna element 30looks like a short circuit in the PCS band, and the PCS antenna element40 looks like an open circuit in the cellular band. In one particularimplementation of this embodiment, the length of the segment 70B is anodd multiple of a quarter wavelength at cellular frequencies, therebytransforming the short circuit presented by the PCS antenna element 40into an open circuit. This feed-line length creates acceptable impedancematches for both antenna elements 30, 40, even though they share acommon transmission line. Because of spatial considerations on the base20, a length of three-fourths of a wavelength can be used. In otherembodiments, a different feed-line length may be required to transformthe impedance to an open circuit in the desired band. The feed-linelength for a particular application will vary depending on a number offactors, including, for example, the frequency band for which theantenna elements are tuned and the size and type of material used forthe base.

The feed line 70 can be further modified to create an impedance matchwith the antenna elements 30, 40. For example, the width of the feedline 70 can be selected to achieve a desired impedance (e.g., 50 Ohms).As understood by one of ordinary skill in the art, the size and shape ofthe antenna elements 30, 40 may need to be adjusted in order to accountfor the impedance created by the feed line 70. Further, although thefeed line 70 in FIGS. 2 and 4 is shown on the bottom of the PCB board,the feed line 70 and the transmission line can be located on the top ofthe base 20. In other embodiments, the antenna elements 30, 40 can bedriven by multiple feed lines, or additional antenna elements can beincluded on the base 20 and driven by the single transmission line 70,which can be adjusted according to the principles described above.

As shown in FIGS. 1-3, antenna element 60 is a third, or additional,antenna element positioned on the upper surface 22 of the base 20. Thethird antenna element 60 can be connected to the upper surface 22 withan adhesive or other suitable means. In the illustrated embodiment,antenna element 60 comprises a global positioning system (GPS) modulecomprising a GPS receive antenna and amplifier. Antenna element 60,however, can comprise a variety of other antennas or electricalcomponents. For instance, antenna element 60 can be an antenna forvarious other applications, including, but not limited to: satelliteradio, PCS, AMPS, TACS, NMT, IS-54/-136, IS-95, GSM, DSC18000, PDC,CDPD, RAM-Mobitex, Ardis-RD-LaP, Bluetooth, or IEEE 802.11. In theillustrated embodiment, antenna element 60 is positioned on the board 20between the first antenna element 30 and the second antenna element 40.In this position, the third antenna element 60 experiences improvedelectrical isolation from the antenna elements 30, 40, and the platformedges 39, 49, which tend to be active areas of radiation on theplatforms 32, 42. Also, isolation between first antenna element 30 andthe second antenna element 40 improved by their being separated from oneanother on the base 20.

In the illustrated embodiment, the third antenna element 60 iselectrically coupled to a separate transmission line (not shown)independent of the feed line 70. The transmission line for the thirdantenna element 60 can be connected to the third antenna element 60 viaapertures 82 shown in FIGS. 2 and 4. Accordingly, in the illustratedembodiment, the antenna 10 is connected to two separate transmissionlines. The illustrated arrangement with the third antenna element 60 isnot limiting, however, and various other arrangements are possible. Forexample, multiple additional antennas can be positioned on the base 20at various locations around or between antenna elements 30, 40. Theseadditional antennas can be used for a variety of applications, such asthose listed above.

FIG. 8 shows a graph of the electrical isolation exhibited in anexemplary antenna 10. The exemplary antenna 10 is substantiallyidentical to the one illustrated in FIGS. 1-4. The first antenna element30 of the exemplary antenna 10 is tuned for the cellular band (i.e.,substantially between 824-894 Mhz>, and the second antenna element 40for the PCS band (i.e., substantially between 1850-1990 Mhz). The thirdantenna element 60 of the exemplary antenna 10 is a GPS receive antenna.Vertical axis 120 of the graph delineates the amount of electricalisolation in decibels of the first and second antenna elements 30, 40versus the third antenna element 60 (labeled on FIG. 8 as “Cellular/PCSto GPS Isolation (dB)”). Horizontal axis 122 delineates the frequencytested in MHz. Plotted line 124 shows the results of the test for theexemplary antenna 10. A first benchmark 130 is shown in the cellularfrequency range as having an electrical isolation limit of −60 dB. Thefirst benchmark 130 represents a desired electrical isolation such asmay be required by an automobile manufacturer or other manufacturer withwhose products the antenna 10 might be used. A second benchmark 132 isshown in the PCS frequency range as having an electrical isolation limitof −40 dB. Like the first benchmark 130, the second benchmark 132represents a desired electrical isolation such as may be required by aproduct manufacturer. As can be seen by plotted line 124, the electricalisolation of the exemplary antenna 10 is well within the limits set bythe first and second benchmarks 130, 132, indicating that the antenna 10exhibits better-than-desired electrical isolation in the PCS andcellular bands. At certain frequencies between the first and secondbenchmarks 130, 132, however, the exemplary antenna 10 experiences lessisolation. Because the exemplary antenna 10 is designed to operate inthe PCS and cellular bands, however, the suboptimal isolation at otherfrequencies is of no importance.

The antenna 10 described above can be utilized for a variety ofapplications in which it is desirable to have a compact antenna. Forinstance, the antenna 10 can be used as part of a telematics system inan automobile. On account of its compact design, the antenna 10 can belocated in numerous areas of the vehicle, including areas hidden fromview of the driver, passenger, and/or outside onlookers.

In the embodiment illustrated in FIGS. 5-7, for instance, the antenna 10is positioned within a roof rack of an automobile. FIG. 5A shows aperspective view of one particular embodiment of the antenna 10integrated into a roof rack 90. As is well known in the art, the roofrack 90 is mounted onto an exterior roof panel 102 of an automobile 100.FIG. 5A shows the roof rack 90 as it terminates near the right, frontcorner of the roof panel 102. Also shown in FIG. 5A is a top of apassenger door 104. The roof rack 90 includes a base portion 96 and acover portion 94. In the illustrated embodiment, the cover portion 94 isdetachably connected to the base portion 96. Together, the cover portion94 and the base portion 96 form a compartment within which the antennahousing 110 is positioned, as shown through the partial cutaway in thecover portion 94. The antenna housing 110 can comprise a plastic housingthat houses the antenna 10 according to one of the embodiments describedabove. The antenna housing 110 can be sealed, except for an antennahousing aperture (not shown) through which the transmission line(s)extend. The antenna housing 110 serves to provide additional support tothe antenna 10 and offers increased protection from outside elementsthat might otherwise harm the antenna 10. The roof rack 90 can beconstructed from a hard plastic, or other suitably sturdy material, andcan further comprise cross beams 92 on which various loads can besecured. The exact dimensions and shape of the roof rack 90 can varywidely depending on the particular application and vehicle.

The distance between the antenna housing 110 and the roof panel 102 canvary from vehicle to vehicle. For instance, in some implementations, theroof panel 102 can be constructed from a metal that forms a capacitivecoupling with the antenna elements 30, 40, 60 of the antenna 10. Inthese embodiments, the base portion 96 of the roof rack 90 can be formedto hold the antenna housing 10 at a distance above the roof panel 102sufficient to facilitate optimizing the impedance match. Alternatively,the roof panel 102 can be used to form part of the ground plane withwhich the antenna elements 30, 40, 60 interact.

FIG. 5B illustrates another embodiment of the integrated roof rack 90.In this embodiment, an additional antenna housing 111 is positionedwithin the compartment formed between the cover portion 94 and the baseportion 96. In the illustrated embodiment, the additional antennahousing 111 is positioned behind the antenna housing 110, but in otherembodiments can be positioned in a variety of locations in the roof rack90. The additional antenna housing 111 can comprise any of the disclosedantennas or any other suitable antenna, and can be coupled with thetelematics or other electronic system of the vehicle in any of themanners described below. For example, antenna housing 111 can contain aBluetooth or IEEE 802.11 antenna configured to communicate with alocal-area network. Thus, the antenna in the antenna housing 111 canoperate in conjunction with an onboard computer to perform electronicbusiness transactions (e.g., make payments at a gas station or tollbooth) or to transfer information (e.g., downloading or uploadingdigital videos, music, or other data (including, for example, vehiclediagnostic data)) wirelessly.

In other embodiments, a plurality of additional antenna housings 111 areincluded in the roof rack 90. The additional antenna housings 111 can belocated in a variety of locations in the roof rack 90 (e.g., in aportion of the roof rack 90 at an opposite side of the roof panel 102).In still other embodiments, any or all of the antennas located withinthe roof rack 90 are not separately enclosed within an antenna housing.Further, as more fully described below with respect to the antennahousing 110, any of the additional antenna housings can be installedduring the actual assembly of the vehicle or at a post-assemblyinstallation point (e.g., a vehicle dealership). Thus, the additionalantenna housing 111 can be one of many possible modules that can beinstalled, swapped, replaced, or removed from the roof rack 90. Thismodular approach creates a wide range of possible antennaconfigurations, which can be individually specified by the manufacturer,dealer, or purchaser.

Two representative implementations of the integrated roof rack 90 andantenna 10 are shown in FIGS. 6A-C and 7. FIG. 6A shows a cross sectionof a first representative implementation at a location on the roof rack90 indicated by arrows 6A in FIG. 5A. FIG. 6B shows a side view of thefirst representative implementation. FIG. 6C shows a top view of theroof rack 90 according to the first representative implementation. Thecover portion 94 includes a support portion 98 on which the antennahousing 110 is placed. The transmission line(s) 116 coupled to theantenna 10 pass through an aperture of the support portion 98. The baseportion 96 further includes ridges 106 that help position the antennahousing 110. The cover portion 94 can attach to the base portion 96 viafrictional tongues 95 and slots (not shown). Alternatively, the coverportion 94 can be attached to the base portion 96 by threaded fastenersor other suitable means. The base portion 96 can also include anextension 114 that extends through an aperture in the roof panel 102 andfurther secures the base portion 96 to the roof panel 102. The extension114 can have a hollow interior through which the transmission line(s)extend and can be a threaded fastener (e.g., a threaded rivnut).

In the first implementation illustrated in FIGS. 6A-C, the antennahousing 110 is positioned above and out of direct contact with the roofpanel 102. During assembly of the vehicle, the roof rack 90 of thisimplementation can be positioned and secured to the roof panel 102 priorto the insertion and wiring of the antenna housing 110. Consequently,the antenna housing 110 can be inserted and wired during the actualassembly of the vehicle, or, in one particular embodiment, at apost-assembly installation point. For instance, the vehicle 100 can beassembled to have a roof rack 90 and transmission line end(s) thatextend through the roof panel 102 into the enclosure of the roof rack 90designed for the antenna housing 110. A customer can then choose among avariety of different antenna housings 110, each offering a differentcombination of antennas and features, and have the selected antennahousing 110 installed, updated, or replaced. Because the internal wiringis already in place, installation of the selected antenna housing 110 isgreatly simplified and can be performed without any additionalmodifications to the vehicle.

FIG. 7 shows a second representative implementation of the integratedroof rack 90 and antenna 10. In the embodiment shown in FIG. 7, theantenna housing 110 directly contacts the roof panel 102 of the vehicle100. The lower base portion 96 of the roof rack 90 does not include asupport portion 98, but instead includes an opening along the bottom ofthe roof rack 90 configured to receive the antenna housing 110. In theillustrated embodiment, for instance, the lower base portion 96 includesridges 106, 108 that surround and position the antenna housing 110within the roof rack 90. The antenna housing 110 can include an antennahousing aperture (not shown) positioned adjacent to a roof panelaperture 112. The transmission line(s) 116 can pass from an interiorspace in the vehicle (e.g., the headliner), through the roof panelaperture 112, and into the antenna housing 110 where the transmissionline(s) 116 are coupled to the antenna 10. The antenna housing 110 canalso include an extension 114 positioned around the antenna housingaperture. The extension 114 can be a hollow, threaded fastener (e.g., athreaded rivnut) that allows passage of the transmission line(s) andsecures the antenna housing 110 to the roof panel 102. In one particularimplementation, the roof panel aperture 112 is formed during assembly ofthe vehicle, and the antenna housing 110 is secured to the aperture 112.When installed on the roof panel 102, the roof rack covers and protectsthe antenna housing 110. A variety of different roof racks 90 can beused to cover the antenna housing 110.

The embodiments of the roof rack 90 described above are not limiting,and can be modified in a number of ways. For instance, the antenna 10may not be enclosed within an antenna housing 110. Instead, the antenna10 can be coupled directly to the base portion 96 or to the roof panel102. Alternatively, the antenna housing 110 can be located in anotherarea of the roof rack. For example, the antenna housing 110 might belocated toward the back end of the roof rack 90. Moreover, the roof rack90 can include multiple antenna housings 110, each of which comprises adifferent combination of antennas 10 or antenna elements.

FIG. 9 shows an embodiment in which the antenna 10 is located in ahousing 110 that is positioned near a rearview mirror 144 and a frontwindshield 140 of a vehicle. In the particular embodiment illustrated inFIG. 9, for instance, the antenna housing 110 is located in a portion ofthe headliner 142 that extends over a portion of the front windshield140 and the roof panel 102. This embodiment is not limiting, however,and the antenna housing 110 can be located in other structures orenclosures adjacent to the rearview mirror 144. In one alternativeembodiment, for instance, the antenna 10 is located in the housingcontaining the rearview mirror 144.

In view of the many possible implementations, it will be recognized thatthe illustrated embodiments include only examples and should not betaken as a limitation on the scope of the disclosed technology. Rather,the disclosed technology is defined by the following claims. Wetherefore claim all embodiments that come within the scope of theseclaims.

1. A compact, vehicle-mounted antenna, comprising: a base having anupper surface, the upper surface of the base being at least partiallycovered with a conductive material, thereby forming a ground plane; andan antenna element positioned on the upper surface of the base, theantenna element comprising: a platform substantially parallel to andspaced apart from the ground plane, a ground connecting the ground planeto an end of the platform, the ground extending from the ground plane atan angle substantially perpendicular to the upper surface of the base,and a feed connecting the base to the platform, a portion of the feedbeing slanted relative to the base as the feed extends from the basetoward the platform.
 2. The antenna of claim 1, wherein a distancebetween the ground plane and the platform is larger than a correspondingdistance in an equivalent planar-inverted-F antenna.
 3. The antenna ofclaim 1, wherein the antenna element is configured to transmit andreceive electromagnetic waves in a band substantially between about 1850and about 1990 MHz.
 4. The antenna of claim 1, wherein the angle of thefeed is adjusted so that the antenna element has a desired height. 5.The antenna of claim 1, wherein the end of the platform is aninward-facing end, the platform further comprising an oppositeoutward-facing end that extends beyond an edge of the base.
 6. Theantenna of claim 5, wherein the outward-facing end forms a capacitivecoupling with a fringe field at the edge of the ground plane.
 7. Theantenna of claim 1, wherein the antenna element is a first antennaelement, the platform is a first platform, the ground is a first ground,and the feed is a first feed, the antenna further comprising: a secondantenna element positioned on the upper surface of the base, the secondantenna element comprising: a second platform substantially parallel toand spaced apart from the ground plane, a second ground connecting theground plane to an end of the second platform, and a second feedconnecting the upper surface of the base to the second platform.
 8. Theantenna of claim 7, wherein the first and second antenna elements arepositioned on opposite halves of the base.
 9. The antenna of claim 8,wherein the first and second antenna elements have outward-facing endsthat are directed substantially parallel to, but opposite of each other.10. The antenna of claim 7, wherein the first and second antennaelements are substantially height matched.
 11. The antenna of claim 1,further comprising an additional antenna element positioned on the uppersurface of the base.
 12. The antenna of claim 11, wherein the additionalantenna element is part of a global positioning system (GPS) receiveantenna.
 13. The antenna of claim 11, wherein the additional antennaelement is part of a satellite radio receiver.
 14. The antenna of claim1, wherein the antenna is positioned within a portion of a roof rack ofa vehicle.
 15. The antenna of claim 14, wherein the antenna is enclosedwithin an antenna housing, and the roof rack portion has a recess shapedto receive the antenna housing when the roof rack and the antennahousing are installed.
 16. The antenna of claim 1, wherein the antennais positioned within and enclosed by a housing, the housing beinglocated near a rearview mirror assembly of a vehicle.
 17. An antennaelement for use in a compact, vehicle-mounted antenna, comprising: asingle conductive strip, the conductive strip being bent and overlappedto form a platform, a sloped segment, and an approximately verticalsegment, the conductive strip being configured to transmit and receiveelectromagnetic transmissions in a predetermined band.
 18. A compact,vehicle-mounted antenna, comprising: a ground conductor; and an antennaelement coupled to the ground conductor, the antenna element having aplatform substantially parallel to and spaced apart from the groundconductor, the platform having a radiating lip that projects outwardlyover an edge of the ground conductor by a predetermined distance, theplatform being supported above the ground conductor by a ground and afeed, wherein the radiating lip forms a capacitive coupling with theedge of the ground conductor, the capacitive coupling partiallycontributing to an impedance of the antenna element.
 19. The antenna ofclaim 18, wherein the predetermined distance is selected to partiallycontribute to the impedance of the antenna element such that theimpedance creates an impedance match with a transmission lineelectrically coupled to the antenna element when the antenna element istuned to a desired frequency.
 20. A compact, vehicle-mounted antenna,comprising: a first antenna element configured to transmit and receiveelectromagnetic transmissions in a first band, the first antenna elementhaving a first feed; a second antenna element configured to transmit andreceive electromagnetic transmissions in a second band different thanthe first band, the second antenna element having a second feed; and aconductive feed line electrically coupling a transmission line to thefirst feed and the second feed, wherein a length of the feed linebetween the first feed and the second feed creates an impedance suchthat the second antenna element appears to be substantially an opencircuit in the first band.
 21. The multiband antenna of claim 20,further comprising at least one additional antenna positionedsubstantially between the first antenna element and the second antennaelement, the additional antenna being configured to at least one ofreceive and transmit electromagnetic transmissions in one or moreadditional bands.
 22. The multiband antenna of claim 21, wherein the atleast one additional antenna is a global positioning system (GPS)receive antenna.
 23. The multiband antenna of claim 20, wherein thefirst and second antenna elements are attached to a base, and whereinone of the first and second antenna elements has a radiating lip thatprojects beyond the base.
 24. The multiband antenna of claim 20, whereinthe feed line has a width selectively adjusted to match the impedance ofa transmission line electrically coupled to the feed line.
 25. Themultiband antenna of claim 20, wherein the first band is between about824 and about 894 MHz, and the second band is between about 1850 andabout 1990 Mhz.
 26. The multiband antenna of claim 20, wherein theantenna is positioned within a portion of a roof rack of a vehicle. 27.The multiband antenna of claim 26, wherein the antenna is enclosedwithin an antenna housing that positioned within the roof rack portion.28. The multiband antenna of claim 20, wherein the antenna is positionedwithin and enclosed by a housing, the housing being located near arearview mirror assembly of a vehicle.
 29. A vehicle-mounted, multibandantenna, comprising: a base having a conductive ground surface; a firstantenna element positioned on the base and being configured to receiveand transmit electromagnetic radiation in a first band, the firstantenna element comprising a first support, a first feed, and a firstplatform substantially parallel to and spaced apart from the groundsurface, the first platform having an inward-facing end and anoutward-facing end; a second antenna element positioned on the base andbeing configured to receive and transmit electromagnetic radiation in asecond band different than the first band, the second antenna elementcomprising a second support, a second feed, and a second platformsubstantially parallel to and spaced apart from the ground surface, thesecond platform also having an inward-facing end and an outward-facingend, the first and second antenna elements being positioned on the basesuch that the outward-facing ends of the first and second antennaelements face substantially opposite directions; and at least oneadditional antenna element positioned substantially between the firstantenna element and the second antenna element, the additional antennaelement being configured to receive and/or transmit electromagneticradiation in one or more additional bands.
 30. The antenna of claim 29,wherein the first antenna element and the second antenna element arepositioned in axial alignment with one another.
 31. The antenna of claim29, wherein the first feed and the second feed are electrically coupledto a transmission line via a single feed line.
 32. The antenna of claim31, wherein the single feed line is located on the lower surface of thebase, and wherein a segment of the feed line between the first feed andthe second feed creates an impedance such that the second antennaelement appears to be substantially an open circuit in the first band.33. The antenna of claim 29, wherein a portion of the second feed of thesecond antenna element is angled such that the second antenna elementhas a desired height and remains configured to transmit and receiveelectromagnetic radiation in the second band.
 34. The antenna of claim33, wherein the second antenna element is height matched with the firstantenna element.
 35. The antenna of claim 33, wherein the angled portionof the second feed is angled away from the second support.
 36. Theantenna of claim 33, wherein the first antenna element is aplanar-inverted-F antenna.
 37. The antenna of claim 29, wherein theadditional antenna element is a global positioning system (GPS) receiveantenna.
 38. The antenna of claim 29, wherein the additional antennaelement is a satellite radio receiver.
 39. The antenna of claim 29,wherein the first band is substantially between about 824 and about 894MHz, and the second band is substantially between about 1850 and about1990 MHz.
 40. The antenna of claim 29, wherein the outward-facing end ofthe second antenna element extends beyond an edge of the ground surfaceand forms a capacitor with the edge of the ground plane, the capacitanceof the capacitor contributing to an impedance of the second antennaelement.
 41. The antenna of claim 40, wherein the capacitance isselectively adjusted to create an impedance match with a transmissionline.
 42. The antenna of claim 29, wherein the antenna is positionedwithin a portion of a roof rack of a vehicle.
 43. The antenna of claim42, wherein the antenna is enclosed within an antenna housing that ispositioned within the roof-rack portion.
 44. The antenna of claim 29,wherein the antenna is positioned within and enclosed by a housing, thehousing being located near a rearview mirror assembly of a vehicle. 45.A vehicle-mounted, communicating antenna, comprising: a first antennaelement for communicating over a first wavelength range; a secondantenna element for communicating over a second wavelength rangedifferent from the first wavelength range, the second antenna elementbeing separated from and in general axial alignment with the firstantenna element; and a third antenna element positioned between and ingeneral axial alignment with the first and second antenna elements. 46.The antenna of claim 45, wherein the first and second antenna elementsare oppositely oriented to increase electrical isolation relative toeach other.
 47. The antenna of claim 45, wherein the first and secondantenna elements are tuned, shaped, and/or positioned relative to eachother to reduce loss of performance.
 48. The antenna of claim 45,wherein the signals from the first and second antenna elements arecommunicated as analog signals via a single transmission line to acircuit within the vehicle.